Photoelectric cell



May 25, 1943. A. H. LAMB 2,320,185v

- 'PHOTOELECTRIG CELL Filed April 3, `1942 Patented May 25, 194.3

PHOTOELECTRIC CELL Anthony H. Lamb, Roselle Park, N. J.. assigner toWeston Electrical Instrument Corporation, Newark, N. J., a corporationof New Jersey Application April 3, 1942-, Serial No. 437,602

(Cl. 13G- 89) 24 Claims.

This invention relates to photoelectric cells and particularly tophotoelectric cells -of the barrier layer or current-generating type.

The prior practice in the manufacture of both copper oxide and seleniumphotocells hasbeen' to form the barrier layer between the photosensitivematerial and the outer electrode as a plane surface. The presentinvention contemplates a deliberate deformation of the barrierlayer toincrease the total effective area of the photocell, thereby to increasethe current output, to control the relative sensitivity of the cell tolight y rays approaching from different directions and/or .surfaces atwhich the electric current is gener- Aated by the incident radiations.

An object is` -to provide photocells with either symmetrically ornon-symmetrically ridged or corrugated surfaces to increasethe photocellsensitivity to radiations approaching along an axis normal to thegeneral plane of the photocell or from a direction inclined to thataxis. An object is to provide a photocell having a non-planar activesurface, and more particularly a photocell including a light sensitiveselenium layer upon the plane .surface of aback electrode, the seleniumv layer vbeing of increased thickness at the portions thereof that areto receive a sprayed-on l metallic current collector. A further objectis to provide a photoelectric cell of the selenium type in which the.selenium layer has a` non-planar outer surface including ridge portionsthat are not covered by the applied outer electrode, the

Fig. 2 is af/section throughv the same 'on the.

plane indicated by the line 2-2 of Fig.. 1'. the thickness of eachcomponent layer being exaggerated and not to scale for clarity ofillustration; Fig. 3 is a similar section through another embodiment ofthe invention;

Fig'. 4 is a plan view of another 'embodiment of the invention; and

Fig.,5'is a transverse section throughthe sam on the plane of line 5-5of Fig. 4.

The invention will be described in detail with reference to seleniumtype photocells that comprise a back electrode of iron or an ironLalloy, a'

relatively thin layer of selenium on the back electrode, and an outer,translucent electrode layer of metal or metals that may be applied by asputtering process. As noted above, the drawings are'not to scale as itis "not possible to illustrate the actualrelative thicknesses of thethree essential layers in a transverse section of small size.

In Figs. 1 and 2, the reference numeral I identifies the back electrodethat may be stamped from a thin iron or `iron alloy plate in the usualmanner. The layer 2 ofselenium has a plane lower surface in contact withthe plane unbroken surface of the back electrode I but the seleniumlayer 2 differs from prior practice in that its outer surface is notplanar but is ribbed or corrugated to increase the totalv surface areapresented towards'theincident radiations. As illustrated, thebase-electrode l is circular in outline, and the outer surface of themajor portion of the selenium layer is circumferentially grooved or, asviewed in transverse section along a diametrical plane, is of undulatingor substantially sine wave form. The peripheral edge portion 3' of theselenium is relatively thick, for reasons that will be explained later,and a number of radial grooves or ribs 4 extend from the thick edgeportion 3 to the small central area 5 that is depressed, as shown, oralternatively is elevated above the medial plane of thecircumferentially grooved portion of the selenium. This central area 5may be embossed or indented with an identifying symbol 6 that may be atype identification or the manufacturers trade-mark.

An annulus l of a soft metal or alloy is preferably sprayed upon thethickened rim portion 3 of the selenium layer before the translucentouter electrode layer 8 is applied byI sputtering or in any otherdesired manner. The electrode layer is of molecular or approximatelymolecular thickness.v

The initial steps in the manufacture of photocells embodying theinvention may conform to present practice. The selenium may beplaced onthe base electrode l in powder or pill form, and the assembly heated tothe melting point of the selenium to effect a flow of the selenium overthe surface of the base electrode. The thickness of the selenium layerat this stage may be of the order of a few thousandths of an inch. A dieof desired irregular or non-planarsurface configuration is then pressedupon the selenium.

layer and the assembly is heated to a tempera-.

ture somewhat below the melting point of the selenium to form the cellunit under heat and pressure. The unit is light sensitized at thecompletion of the forming operation, and the. current collector ring 'iand electrode layer 8 are then applied.

It will be apparent that the area of the irregu-.

lar surface of the photocell is substantially larger than the area of aphotocell of the same dimensions and of the conventional at surfacetype, and-that the current output for a given illumination is therebyincreased. The shape and dimensionsnf the surface irregularities may bevaried as desired in accordance with the desired photocellcharacteristics. 'I'he thickness of the selenium layer 2 may be, forexample, about 0.001 inch at the thinner sections and about 0.020 inchat the ribbed or thicker sections. v

The fiat radial grooves or ribs 4 provide channels of low electricalresistance from the interior portion of the photocell to the outer edgeportion to which a terminal connection is to be made. The translucentelectrode layeris of relatively high resistance and the currentdeveloped at the center of the photocell would be forced to travel upand down the undulating electrode layer 8 to reach the cell periphery ifthe shorte length channels were omitted.

yThe grooves of the irregular photocell surface may be nlled with atransparent lacquer or resin 9 that reinforces the cell structure andincreases the total current output by a reflection of the radiationsfrom one surface or slope of the photocell ridges to another.

The additional thickness of the selenium layer 3 at the cell peripheryreduces the possibility of a short-cireuiting of the cell by apenetration of the sprayed current collector l through the seleniumlayer, and increases the internal resistance of the cell. y

The dimensions and shape of the non-planar elements of the seleniumlayer may be Varied in accordance with lthe desired characteristics ofthe cell. .As shown in Fig. 3, the outer surface of the selenium layer2a may comprise sets of plane surfaces of different widths that areangularly arranged and non-symmetrical with respect to a plane normal tothe mean surface of they selenium surface. A photocell with asaw-toothed surface of this type will have a maximumv response to thoserays, as indicated by the arrows a, that are substantially normal to thelarger area elements of the non-planar surface. TheY directionalsensitivity of the photocell may be controlled by an' appropriate designof the non-symmetrical ridges and grooves of the selenium layer. Thisform of the invention is well adapted for use in illuminationcontrolling systems in which lights are to be turned on when the `solarillumination falls below some selected value. The photocell may bearranged vertically in a protective housing and have the northern skysensitivity that was previously obtained by tilting the photocell.,

Furthermore, the\nonplanar selenium latter:V

may be shaped to provide a self-contained. iiie for'limiting theacceptance angle of the photocell. In the embodiment shown in Figs. 4and 5, the selenium layer 2b is die pressed during the forming operationto provide upstanding ridges l2 of generally hexagonal contour, asviewed in plan, but with gaps I4 in the ridges or hexagonal compartmentwalls. The translucent electrode' layer 8a is not applied to the sidesand tops of the ridges but overlies the bottom of each hexagonal welland is continuous through the gaps I4 to form-low resistance connectionsbetween the electrode layers within the hexagonal compartments and theelectrode layer that extends over the current collector ring 1. Thedimensions of the ridges I2 may be suchas t'o provide the desiredacceptance angle limitation or to cooperate with superposed optical ormechanical baiiie members, not shown, of small thickness, to establishthe desired acceptance angle of the photocell.

Photocells or photocell assemblies have been proposed in which seleniumlayers 4of uniform thickness were applied to a back electrode orelectrodes of non-planar form but it is broadly new. so far as nowknown, to impart a non-planar surface conguration to the outer surfaceof the thin layer of selenium or other, photosensitive' material on-aatplate back electrode. Itis therefore to be understood that the inventionis not limited to the particular embodiments herein shown and described,and that various changes that may occur to those skilled in the art fallwithin the scope of my invention as set forth in the following claims.

i. A current generating photocell of the type comprising a backelectrode, a llayer of photosensitive material on said back electrode,and a translucent electrode overlying the photosensitive materiallaye'r, characterized b y the fact that the outer surface of thephotosensitive material layer is non-planar.

2. A current generating photocell as recited invclaim 1, wherein thenon-planar outer surface of the photosensitive material layer isundulating as viewed iii-transverse section. L

3. A current generating photocell as recited in claim 1, wherein thenon-planar outer surface of the photosensitive material layer isundulating and .of approximately sine wave form as viewed in transversesection.

4. A current generating photocell as recited in claim 1, wherein thenon-planar outer surface of the photosensitivematerial layer isconstituted by lnarrow angularly arranged plane surface elements. Y

5. A current generating photocell as recited in claim '1, wherein thenon-planar outer Surface of the photosensitive material layer isconstituted by narrow angularly arranged plane surface elements, theadjacent surface elements being arranged non-symmetrically with respectto a plane normal to the mean plane of the irregular surface of thephotosensitive material layer.

6. In a photoelectri'c cell, a plane surfaced back electrode, a layer ofphotosensitive material upon the plane surface of said back electrode,and an outer electrode layer. upon the photosensitive material layer,theboundary surface between said photosensitive'material layer and saidouter electrode layer being non-planan.

1. In -a photoelectric cell, the-invention as recited in claim 6 whereinthe non-planar outer l 2,320,185 lsurface. of said photosensitivematerial lay-er is impressed with ribs and grooves.

8. In a photoelectric cell, the invention as recited in claim 6 whereinthe non-planar outer surface of said photosensitive material layerisimpressed with ribs and grooves having surfaces non-symmetrical withrespect to a plane normal to the mean plane of the irregular surface ofthe photosensitive material layer.

"9. In a photoelectric cell, a back electrode. a layer of photosensitivematerial on said back electrode, the outer surface of said layer beingribbed and having plane-surfaced strips extendnon-planar layer ofphotosensitive material on y said base electrode. said non-planarsurface being defined .by upstanding ridges forming the walls defininga`series of compartments 'with gaps inthe ridges, and a translucentelectrode layer extending over the bottoms of the compartments andthrough the gaps of said ridges.

the sides and tops of the ridges being free from said electrode layer toform bailies for determining the acceptance angle of the cell..

18. In a photoelectric cell, a back electrode, a

.layer-.of photosensitive material on said electrode and having a ribbedouter surface, a translucent ing across the ribs, and a translucentelectrode Ilayer extending over said photosensitive material layer.

10. In a photoelectric cell. a back electrode.

electrode, said layer having an identifyingdesign impressed thereon, anda translucent outer electrode layer extending over said photosensitivematerial layer.

ll. In a photoelectric cell, the invention as recited in claimv10.`wherein said design is im-l pressedA upon a portion of the outersurface of maining portion of said surface is non-planar.

12. In a photoelectric cell,`the invention as recited in,claim 10,wherein said design is impressed upon a portion of the outer surface'ofI a layer of photosensitive material on said back.

-said photosensitive material layer, and the re-' said photosensitivematerial layer, and the remaining portion of said surface is ribbed.

13. In a photoelectric cell, a back'electrode 'with a .plane unbrokenupper surface,'a layer of selenium on said surface and thickened at theperiphery thereof, a current collector sprayed upon said thickenedperiphery of the selenium layer, and a translucent electrode layeroverelectrode layer over-said photosensitive material layer, andtransparent material nlling theY grooves of the photocell.

i9. In the manufactureof aphotoelectric cell of the type including alayer of photosensitive ,material between a back electrode and an outertranslucent electrode, the method of increasing the photocell output ata given illumination which comprises shaping the boundary between saidphotosensitive material and said layer as a non-planar surface.

20. The process of making a photoelectric cel that comprises applying alayer of selenium to a at back electrode, die shaping the seleniumlayertoimpart to the outer surface thereof a non-planar configuration,and applying a trans- `lucent electrode layer to the irregular outersur-v face ofthe selenium layer. u

21. Ihe process of making a photoelectric cell that comprises applying alayer of selenium to a flat back electrode, die shaping the seleniumlayer to forma thickened portion at the periphery thereof, and applying,an outer translucent electrode layer over the selenium layer.

22. The process of making a photoelectric cell that comprises applyingalayer of selenium to a flat back electrode, die shaping the selenium vlayer to form a thickened portion atV tle petion with a depressedcentral portion anda v ribbedportion extending from the depressedcentral portion to the thickened periphery.

16. In a photoelectric cell, the .invention as of the selenium layer isof irregular configuration with a depressed central portion and a ribbedportion extending from the depressed central'portion to the thickenedperiphery, said central portion being impressed with'an idenl tifylns'symbol.

l'l. In a photoelectric cell, a base electrode. a

i claimed-m claim is wherein the outer sui-:cee`

riphery thereof. spraying metal upon the thickened outer portion of theselenium layer, and applylnga translucent electrode layer over theselenium and the sprayed-on metal.

23. In the manufacture of a photoelectric cel1,

fthe process which comprises forming on a back electrode a layer oflight sensitive material` with upstanding ridges defining compartmentsand applying an-outer electrode layer ofthecompartments.' l

24. In the manufacture of a photoelectric cell. the process whichcomprises forming on a back to thebottms electrode a layer of lightsensitive material with upstanding discontinuous-.ridges denningcompartments communicating through the-gaps in the ridges. and applyingan outer electrode layer to the vbottoms of thecompartments and the gaps-in said ridges.

' 5\ .xN'rnoNY H. mus.

translucent

